Research On Two-dimensional Displacement Measurement Technology Based On Laser Self-mixing Interference Effect

In the high-demand areas such as integrated circuit manufacturing,semiconductor industry and nanotechnology,higher requirements for high-resolution,high-precision displacement measurement are put forward.In recent years,laser self-mixing interference technology has attracted more and more attention due to its unique compactness,robustness and self-collimation,and is widely used in the field of precision displacement measurement.When a portion of light emitted from a laser source is reflected or scattered back into the laser cavity by an external target,the reflected light will mix with the light inside the cavity,causing a modulation of the laser output power.This phenomenon is called as self-mixing interference(SMI),in which the reflected light carries some information of the external target.Like the traditional two-beam interferometer,laser self-mixing interference technology has the advantages of fast measurement speed,high precision,non-contact,etc.,but it is sensitive to environmental disturbances such as pressure fluctuation,humidity change and laser power instability.In order to achieve a measurement accuracy of nanometers,the working environment must be strictly controlled.The grating interference technique uses the grating pitch as the measurement reference,has lower requirements on environmental factors,and has great advantages in environmental control.In this paper,the laser self-mixing interference effect and the grating interference are combined.By introducing the diffraction grating into the laser self-mixing interference system,the measurement reference of the self-mixing interference changes from the wavelength to the grating pitch of the relatively stable grating,which is greatly improved.The stability of the system,and due to the limitation of diffraction efficiency,the laser feedback interference automatically works under weak feedback conditions,without additional control of the amount of optical feedback.A single-path laser self-mixing grating interferometer was designed for the measurement of in-plane and out-of-plane displacement.The system structure has the advantages of self-collimation,simple structure and easy operation with Littrow configuration,.In order to demodulate the phase of the laser feedback grating interference signal with high precision,the laser self-mixing interference signal is subjected to high-frequency phase modulation by using a lithium niobate electro-optical crystal.The theoretical derivation and simulation analysis of displacement measurement are given in this paper.The simulation results are observed experimentally.Finally,the error source and measurement accuracy of the measurement results are analyzed.The experimental results show that the system has strong anti-interference ability and can achieve a measurement accuracy of tens of nanometers.Based on this research,a symmetrical laser self-mixing grating interference system was developed for two-dimensional displacements measurement of in-plane and out-of-plane direction.The theoretical derivation and simulation analysis of two-dimensional displacement measurement are elaborated,and the simulation results are observed experimentally.Finally,the error source and measurement accuracy of the measurement results are analyzed.The experimental results show that the system can achieve a measurement accuracy of tens of nanometers.The novel laser self-mixing grating interference system not only has the advantages of simple and compact struction no need for external detectors like laser feedback interferometer,but also has the advantages of high measurement accuracy and strong anti-interference ability,it has a good development prospect.